California Code, Government Code - GOV § 1157.3

(a) Employees, including retired employees, of a public employer in addition to any other purposes authorized in this article, may also authorize deductions to be made from their salaries, wages, or retirement allowances for the payment of dues in, or for any other service, program, or committee provided or sponsored by, any employee organization or bona fide association whose membership is comprised, in whole or in part, of employees of the public employer and employees of such organization and which has as one of its objectives improvements in the terms or conditions of employment for the advancement of the welfare of the employees.

(b) The public employer shall honor employee authorizations for the deductions described in subdivision (a).  The revocability of an authorization shall be determined by the terms of the authorization.